x86: Fix zefi.py creating valid images

When zefi.py was changed to pass compiler and objcopy the flag to
objcopy for the EFI target was dropped.  This is because the current
SDK (0.12.1) doesn't support that target type for objcopy.  However,
target is necessary for the images to be created correctly and boot.

Switch back to use the host objcopy as a stop gap fix, until the SDK
can support target for EFI.

Fixes: #31517

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>